问题
I'm using a Scikit-Learn custom pipeline (sklearn.pipeline.Pipeline) in conjunction with RandomizedSearchCV for hyper-parameter optimization. This works great.
Now I would like to insert a Keras model as a first step into the pipeline. Parameters of the model should be optimized. The computed (fitted) Keras model should then be used later on in the pipeline by other steps, so I think I have to store the model as a global variable so that the other pipeline steps can use it. Is this right?
I know that Keras offers some wrappers for the Scikit-Learn API but the problem is that these wrappers already do classification / regression but I only want to compute the Keras model and nothing else.
How can this be done?
For example I have a method which returns the model:
def create_model(file_path, argument2,...):
...
return model
The method needs some fixed parameters like a file path etc. but X and y is not needed (or can be ignored). The parameters of the model should be optimized (number of layers etc.).
回答1:
You need to wrap your Keras model as a Scikit learn model first, and then just proceed as normal.
Here's a quick example (I've omitted the imports for brevity)
Here is a full blog post with this one and many other examples: Scikit-learn Pipeline Examples
# create a function that returns a model, taking as parameters things you
# want to verify using cross-valdiation and model selection
def create_model(optimizer='adagrad',
kernel_initializer='glorot_uniform',
dropout=0.2):
model = Sequential()
model.add(Dense(64,activation='relu',kernel_initializer=kernel_initializer))
model.add(Dropout(dropout))
model.add(Dense(1,activation='sigmoid',kernel_initializer=kernel_initializer))
model.compile(loss='binary_crossentropy',optimizer=optimizer, metrics=['accuracy'])
return model
# wrap the model using the function you created
clf = KerasRegressor(build_fn=create_model,verbose=0)
# just create the pipeline
pipeline = Pipeline([
('clf',clf)
])
pipeline.fit(X_train, y_train)
回答2:
This is a modification of the RBM example in sklearn documentation (http://scikit-learn.org/stable/auto_examples/neural_networks/plot_rbm_logistic_classification.html#sphx-glr-auto-examples-neural-networks-plot-rbm-logistic-classification-py)
but the neural network implemented in keras with tensorflow backend
# -*- coding: utf-8 -*-
"""
Created on Mon Nov 27 17:11:21 2017
@author: ZED
"""
from __future__ import print_function
print(__doc__)
# Authors: Yann N. Dauphin, Vlad Niculae, Gabriel Synnaeve
# License: BSD
import numpy as np
import matplotlib.pyplot as plt
from scipy.ndimage import convolve
from keras.models import Sequential
from keras.layers.core import Dense,Activation
from keras.wrappers.scikit_learn import KerasClassifier
from keras.utils import np_utils
from sklearn import datasets, metrics
from sklearn.model_selection import train_test_split
from sklearn.neural_network import BernoulliRBM
from sklearn.pipeline import Pipeline
#%%
# Setting up
def nudge_dataset(X, Y):
"""
This produces a dataset 5 times bigger than the original one,
by moving the 8x8 images in X around by 1px to left, right, down, up
"""
direction_vectors = [
[[0, 1, 0],
[0, 0, 0],
[0, 0, 0]],
[[0, 0, 0],
[1, 0, 0],
[0, 0, 0]],
[[0, 0, 0],
[0, 0, 1],
[0, 0, 0]],
[[0, 0, 0],
[0, 0, 0],
[0, 1, 0]]]
shift = lambda x, w: convolve(x.reshape((8, 8)), mode='constant',
weights=w).ravel()
X = np.concatenate([X] +
[np.apply_along_axis(shift, 1, X, vector)
for vector in direction_vectors])
Y = np.concatenate([Y for _ in range(5)], axis=0)
return X, Y
# Load Data
digits = datasets.load_digits()
X = np.asarray(digits.data, 'float32')
X, Y = nudge_dataset(X, digits.target)
X = (X - np.min(X, 0)) / (np.max(X, 0) + 0.0001) # 0-1 scaling
X_train, X_test, Y_train, Y_test = train_test_split(X, Y,
test_size=0.2,
random_state=0)
#%%
def create_model():
model = Sequential()
model.add(Dense(100, input_dim=64))
model.add(Activation('tanh'))
"""
#other layer
model.add(Dense(500))
model.add(Activation('tanh'))
"""
model.add(Dense(10))
model.add(Activation('softmax'))
# Compile model
model.compile(loss = 'binary_crossentropy', optimizer = 'adadelta', metrics=['accuracy'])
return model
rbm = BernoulliRBM(random_state=0, verbose=True)
#This is the model you want. it is in sklearn format
clf = KerasClassifier(build_fn=create_model, verbose=0)
classifier = Pipeline(steps=[('rbm', rbm), ('VNN', clf)])
#%%
# Training
# Hyper-parameters. These were set by cross-validation,
# using a GridSearchCV. Here we are not performing cross-validation to
# save time.
rbm.learning_rate = 0.06
rbm.n_iter = 20
# More components tend to give better prediction performance, but larger
# fitting time
rbm.n_components = 64
#adapt targets to hot matrix
yTrain = np_utils.to_categorical(Y_train, 10)
# Training RBM-Logistic Pipeline
classifier.fit(X_train, yTrain)
#%%
# Evaluation
print()
print("NN using RBM features:\n%s\n" % (
metrics.classification_report(
Y_test,
classifier.predict(X_test))))
#%%
# Plotting
plt.figure(figsize=(4.2, 4))
for i, comp in enumerate(rbm.components_):
plt.subplot(10, 10, i + 1)
plt.imshow(comp.reshape((8, 8)), cmap=plt.cm.gray_r,
interpolation='nearest')
plt.xticks(())
plt.yticks(())
plt.suptitle('64 components extracted by RBM', fontsize=16)
plt.subplots_adjust(0.08, 0.02, 0.92, 0.85, 0.08, 0.23)
plt.show()
来源：https://stackoverflow.com/questions/42415076/how-to-insert-keras-model-into-scikit-learn-pipeline